I was re-watching "316" earlier, when I got to thinking as to why Eloise Hawking was no longer on the Island.
I originally believed that she had been banished, but then I changed my mind to the idea that she left to raise her son Daniel Faraday off-Island.
However, I don't think that is actually the reason.
As we know, Eloise is the reason why the Oceanic 6 knew how to get back to the Island, and these people were supposed to go back to the Island.
But how come Charles couldn't ever get to the Island all of that time.
I believe that Charles could have easily gotten back to the Island, through the means of Eloise, however Jacob did not wish him to return...yet.
I think that Jacob had a hold of Charles and Eloise, and that eventually their destinies would meet again, so that Eloise could get the people who needed to return (perhaps even herself), back to the Island.
(Also, when Charles sent Keamy and the mercenaries to the Island, he didn't go because he couldn't, but only because he was not meant too. Instead, he sent the mercenaries to head to the Island, to capture Ben, because it was a personal vendetta of Charles')
That's all I've got!